Process for the isolation of 1,2,5,6-hexanetetrol from sorbitol hydrogenolysis reaction mixtures using simulated moving bed chromatography

ABSTRACT

A method of isolating and purifying 1,2,5,6 hexanetetrol (HTO) from a reaction mixture containing HTO and other byproducts of a hydrogenation reaction of a sugar alcohol and/or a mono- or di-dehydrative product of a sugar alcohol is described. The method involves contacting the mixture comprising HTO and other C1-C6 alcohols and polyols with a resin material adapted for chromatography under conditions where HTO preferentially associates with the resin relative to other components in the mixture, and eluting HTO from said resin with a solvent.

PRIORITY CLAIM

The present application claims benefit of priority of InternationalApplication Nos. PCT/US2014/033580 and PCT/US2014/033581, both filedApr. 10, 2014.

TECHNICAL FIELD OF INVENTION

The present invention relates to the synthesis and recovery of ahydrogenolysis product using chromatographic techniques. In particular,the invention pertains to the separation and purification of polyolsderived from the hydrogenolysis of C₆ sugar alcohols.

BACKGROUND

In recent years, interest has grown in renewable source-basedalternatives for organic functional materials that can serve asfeedstocks for organic compound that have been made traditionally frompetroleum or fossil-based hydrocarbons. As an abundant bio-based orrenewable-resource, carbohydrates represent a viable alternativefeedstock for producing such materials.

Biomass contains carbohydrates or sugars (i.e., hexoses and pentoses)that can be converted into value added products from renewablehydrocarbon sources. Sugar alcohols, such as sorbitol, mannitol, iditol,arbitol or xylitol, are one kind of sugar-derived compounds that can befurther transformed into various kinds of materials, which in turn canbe further modified.

The molecule 1,2,5,6-hexanetetrol (“HTO”) is a by-product of thehydrogenolysis of sugar alcohols. Over the past century, variousresearchers have worked to prepare 1,2,5,6-HTO. For example, Zartman andAdkins reported in 1933 the synthesis of 1,2,5,6-hexanetetrol(1,2,5,6-HTO) by hydrogenolysis of sorbitol at 250° C. under 300 atm H₂using copper-chromium oxide catalyst. (Zartman W., Adkins H., J. Am.Chem. Soc., 55, 4559 (1933).) In 1958, Gorin and Perlin reported thehydrogenolysis of 1,2-O-isoprpylidene-d-glucofuranose in a stirred batchunder H₂ at 2000-2900 psi at 180° C. for 6 hrs in the presence of copperchromium oxide catalyst and the subsequent separation of 1,2,5,6-HTO byliquid-liquid extraction. (Gorin, P. A. J., Perlin, A. S., CanadianJournal of Chemistry (1958) v. 36, pp. 661-6.) In 1989, Urbas claimedthe synthesis of “3,4-dideoxyhexitol” (1,2,5,6-hexanetetrol) via thecatalytic hydrogenolysis of sorbitol, in a stirred batch reaction using85% CuO and 15% Cr2O3 under 184-150atm H₂ at 200° C. for 3 hrs and thesubsequent acid catalyzed dehydration of 1,2,5,6-HTO to2,5-bis(hydroxymethy)tetrahydrofuran (U.S. Pat. No. 4,820,880).Montassier describes a heterogeneous catalysis of sorbitol by aretro-Michael reaction to selectively yield glycerol from sorbitolfavored on certain copper-based catalysts. (Montassier, C., et. al.,Bulletin de la Societe Chimique de France (1989) (2), 148-55.) Ludwigmentions 1,2,5,6-HTO as a nearly 4% wt by-product in the synthesis ofdiols from sucrose, in a batch reaction, using CoO, CuO, Mn3O4, H₃PO₄,and MoO₃ at 160C, under 280 bar H₂, for three hours but does not claimany methods for purification of the 1,2,5,6-HTO (DE 3928285 A1). Cargillmentions it as an impurity in a patent for the purification of sorbitolhydrogenolysis reactions using sweep gas (International PatentApplication No. WO08057263). In 1997, Maier reported selective catalyticsynthesis of 1,2,5,6-HTO by double asymmetric dihydroxylation of1,5-hexadiene in one step, with purification of the meso compound byliquid-liquid extraction. (Maier, M. E., Reuter, S., LiebigsAnnalen/Recueil (1997) (10), 2043-2046.) Also, by direct oxidation ofunsaturated hydrocarbons, Milnas reports the synthesis of 1,2,5,6-HTOwith H₂O₂ in anhydrous tert-butanol in the presence of OsO₄ (Milas, N.A., Sussman, S., J. Am. Chem. Soc., (1937) 59, 2345-7; U.S. Pat. No.2,437,648).

1,2,5,6-HTO and other polyols having fewer oxygen atoms than carbonatoms may be considered a “reduced polyols.” Corma et al. disclosegenerally that higher molecular weight polyols containing at least fourcarbon atoms can be used to manufacture polyesters, alkyd resins, andpolyurethanes. (Corma et al., “Chemical Routes for the Transformation ofBiomass into Chemicals,” 107 Chem. Rev. 2443 (2007)). 1,2,5,6-HTO ismentioned, for example, as a starting material for the synthesis ofdiols (International Patent Application No. WO13163540) and for moreesoteric multistep syntheses of small molecules (See, e.g., Machinaga,N., et al, Journal of Organic Chemistry, 1992, 57, 5178; Fitremann, J.,et al, Tetrahedron, 1995, 51, 9581; Mayumi A., et al., TetrahedronLetters (2000), 41(8), 1199-1203.).

As a useful intermediate in the formation of higher value chemicals, theindustrial production of 1,2,5,6-HTO can be commercially important. Forinstance, 1,2,5,6-HTO is of primary commercial interest as a feedstockfor the synthesis of adipic acid via continuous, selective oxidation.Adipic acid is used industrially to produce polyurethanes, plasticizers,lubricant components, polyester, and as food ingredient. Adipic acid'sprimary industrial outlet is in the production of Nylon-6,6 fibers andresins which, in 2010, accounted for 65% of the di-carboxylic acid'stotal 2.6 MM tons produced globally (See, e,g., Polen, T., et al.,Journal of Biotechnology 167 (2013) 75-84).

Subsequent to the original work by Zartman et al. the literature isrelatively sparse with references to 1,2,5,6-HTO compound, especiallywith regard to its production, isolation and purification. Given therecent increase in interest of using sugar-alcohols as a carbon resourceand the value of 1,2,5,6-HTO as a potential commercial feedstock,various industrial and research entities are beginning to gatherresources to develop better ways of making and separating this compound.Hence, a need exists for a method for isolating and purifying1,2,5,6-HTO from a hydrogenolysis reaction mixture. In particular, aprotocol that can be adapted to high-volume throughput systems would bewelcome.

SUMMARY OF THE INVENTION

The present disclosure describes, in part, a method for the isolationand purification of 1,2,5,6-hexanetetrol (HTO) (C₆H₁₄O₄) from a reactionmixture derived from hydrogenolysis of sugar alcohols. The methodinvolves: contacting a mixture comprising HTO and other C₁-C₆ alcoholsand polyols with a resin adapted for chromatographic use, underconditions where HTO preferentially associates with the resin relativeto other components in the mixture, and eluting HTO from the resin witha solvent. In particular, the resin employed is a non-functionalizedmaterial although other functionalized resin may also be used.

In another aspect of the invention, one can adapt the foregoing conceptfor high-throughput or continuous separations. One can implement asimulated-moving-bed (SMB) chromatographic system for the primaryapplication.

Additional features and advantages of the present purification processwill be disclosed in the following detailed description. It isunderstood that both the foregoing summary and the following detaileddescription and examples are merely representative of the invention, andare intended to provide an overview for understanding the invention asclaimed.

BRIEF DESCRIPTION OF FIGURES

FIG. 1A is a flow chart representing conventional process for preparingand separating polyols from a hydrogenolysis reaction of sorbitol.

FIG. 1B is a flow chart showing an alternative conventional process forpreparing and separating polyols from a hydrogenolysis reaction ofsorbitol.

FIG. 1C is a flow chart illustrating another conventional process forpreparing and separating polyols from a hydrogenolysis reaction ofsorbitol.

FIG. 2 is a flow chart showing a process for preparing and purifying1,2,5,6-HTO from a hydrogenolysis reaction of sorbitol showingdifferences according to an embodiment of the present invention.

FIG. 3 is a graph showing pulse test results for the chromatographicseparation of processed sorbitol hydrogenolysis reaction mixture.

FIG. 4 is a graph showing pulse test results with zones dividinganalytes.

FIG. 5 is a diagram of a 500 cc simulated moving bed (SMB) systemconfigured according to an embodiment of the present invention.

FIG. 6 is a graph showing the percent adsorption vs resin loading forsorbitol from thin-film evaporative (TFE) distillate bottoms.

FIG. 7 is a graph showing the percent adsorption vs resin loading for1,2,5,6-HTO from thin-film evaporative (TFE) distillate bottoms.

FIG. 8 is a graph showing the relative selectivity of a chromatographicresin (e.g., V493) according to an embodiment of the present inventionfor 1,2,5,6-HTO from sorbitol.

FIG. 9 is a graph showing the capacity of a non-functionalized resin(V493) according to an embodiment of the present invention for1,2,5,6-HTO separation.

DETAILED DESCRIPTION OF THE INVENTION Section I—Terminology

Before describing the present invention in detail, it is understood thatthe terminology used to describe particular embodiments is not intendedto be limiting. As used in this specification and the appended claims,the singular forms “a,” “an,” and “the” include the plural referentsunless the context clearly indicates otherwise. Unless defined otherwisein context, all technical and scientific terms used herein have theirusual meaning, conventionally understood by persons skilled in the artto which the present invention pertains.

The term “bed volume” or “column volume” refers to the total volume ofthe packing material and interstitial liquid. The minimum volume ofsolvent necessary to wet the defined quantity of sorbent within thecolumn can vary on the nature of the sorbent (e.g., ˜120 μl per 100 mgof silica gel sorbent 60 Å, compared to ˜600 μl per 500 mg of silica gelsorbent 60 Å).

The term “chromatographic resolution” refers to the degree of separationbetween consecutive analytes emerging from a chromatographic column.

The term “step-time” refers to the interval or dwelling time that achromatographic columns in a simulated-moving bed chromatographic deviceremains at a particular position before the position rotates.

Section II—Description

The present invention describes, in part, a process for the separationand purification of chemicals derived from hydrogenolysis of sugaralcohols. Sorbitol hydrogenolysis is known to produce1,2,5,6-hexanetetrol (HTO) and other polyols, although typically thereaction conditions are harsh and not economical. Various approaches canbe used to make HTO. For instance, U.S. Pat. No. 4,820,880, discloses amethod for producing HTO that involves heating a solution of a hexitolin an organic solvent with hydrogen at an elevated temperature andpressure in the presence of a copper chromite catalyst. Exemplarystarting hexitols include sorbitol and mannitol. Water was found toadversely affect the reaction speed requiring the reaction to beperformed in the absence of water and instead using ethylene glycolmono-methyl ether or ethylene glycol mono-ethyl ether as the solesolvent, which puts a solubility limit on the amount sorbitol that onecan react. Under such conditions the maximum concentration of sorbitolthat had been shown to be useful was 9.4% wt./wt. in ethylene glycolmono-methyl ether, which provided a molar yield of about 28% HTO. In asimilar reaction where the sorbitol concentration was reduced to about2% wt/wt in glycol methyl ether, the molar yield of HTO was 38% howeverthe low concentration of reactants makes mono-such a processuneconomical. U.S. Pat. No. 6,841,085, discloses methods for thehydrogenolysis of 6-carbon sugar alcohols, including sorbitol, involvingreacting the starting material with hydrogen at a temperature of atleast 120° C. in the presence of a rhenium-containing multi-metallicsolid catalyst. Nickel and ruthenium catalysts were disclosed astraditional catalysts for sorbitol hydrogenolysis, however thesecatalyst predominantly produced lower level polyols such as glycerol andpropylene glycol and were not shown to detectably produce HTO orhexanetriols. (The contents of U.S. Pat. Nos. 4,820,880, and 6,841,085,are incorporated herein by reference.)

Other synthesis processes are described in International ApplicationNos. PCT/US2014/033580 and PCT/US2014/033581, the relevant contents ofwhich are incorporated herein by reference. The processes described inthese application involve contacting a solution comprising water and atleast 20% wt/wt of a starting compound selected from the groupconsisting of a C₆ sugar alcohol and a R-glycoside of a C₆ sugar,wherein R is a methyl or ethyl group, with hydrogen and a Raney coppercatalyst for a time and at a temperature and pressure sufficient toproduce a mixture containing one or more of the reduced sugar alcoholswith a combined selectively yield of at least 50% mol/mol. In mostadvantageous embodiments of these methods the reaction solutioncomprises 20-30% wt./wt. water and 45-55% of a C₂-C₃ glycol. In anexemplary embodiment the solution comprises 20-30% wt./wt. water and50-55% wt./wt. propylene glycol. These methods provide a combinedselectivity yield for the reduced sugar alcohols of at least 70%mol/mol. A specific embodiment for making 1,2,5,6-hexanetetrol involvedcontacting a solution comprising 20-30% wt./wt. water, 45-55% ofpropylene glycol and at least 20% wt./wt. of a starting compoundselected from the group consisting of C₆ sugar alcohol and a R-glycosideof a C₆ sugar, wherein R is a methyl or ethyl group, with hydrogen and aRaney copper catalyst for a time and at a temperature and pressuresufficient to produce a mixture containing the 1,2,5,6-hexanetetrol witha selectively yield of at least 35% wt./wt. In most advantageousembodiments the selectivity yield for 1,2,5,6-hexanetetrol is at least40% wt./wt.

A.—Purification Process

Conventional processes for separating and purifying the desired HTO fromother polyols and hydrogenolysis products have involved either complextechniques and/or multistep protocols. FIG. 1A is a flow chart thatillustrates typical standard purification methods. The protocol involvesfirst reacting sorbitol solution 1 in a hydrogenolysis reactor 2,transferring the hydrogenolysis-reaction, polyol-product mixture 3 to anevaporator 4 to drive off water and low-boiling alcohols 4 a (e.g.,methanol and ethanol), then subjecting the resulting dewatered polyolreaction mixture 5 to one or more distillations 6 and collecting thehigh-boiling polyols 6 a (e.g., propylyene glycol (PG), ethylene glycol(EG), glycerol). Finally, the remaining crude bottoms products 7 aresubjected to one or more rounds of crystallization 8 to remove anyresidual higher-boiling polyols and unreacted sugar alcohols 8 a (e.g.,C₆ triols, sorbitol), and produce a concentrated and purified HTOproduct 9. Alternatively, as depicted in FIG. 1B, the evaporator (ordistillations) can be run at a higher temperatures and/or higher vacuumto remove glycerol before crystallization. FIG. 1C illustrates analternative protocol that does not use an evaporator but involvessolvent or liquid-liquid extraction (LLE) technique, in one or moresolute contained in a feed solution is transferred to another immiscibleliquid solvent.

In comparison, the present purification process is simpler involvingless steps or more cost efficient techniques. The present processemploys a resin adapted for chromatographic purposes to separate andpurify HTO from hydrogenolysis reaction mixtures. In certain embodimentsthe present method involves a combination of evaporation andsimulated-moving bed chromatography. FIG. 2 presents a flow chartaccording to an embodiment of the present invention. After reactingsorbitol solution 1 in a hydrogenolysis reactor 2, transferring thehydrogenolysis-reaction, polyol-product mixture 3 to an evaporator 4 todrive off water, low-boiling alcohols, and C₁-C₅ diols 4 a (e.g., MeOH,EtOH, PG, EG, 2,3-PeDO), de-ionized water (DI) 4 b is added to dilutethe polyol mixture 5, which is then subjected to chromatographicseparation 6 using either non-functionalized or functionalized resins.Desirably the separation is performed with a non-functionalized resin ina simulated-moving bed (SMB) chromatographic device. The de-ionizedwater serves to dissolve the mixture and make the solution less viscous.In certain embodiments, it may be possible to use the water from theevaporator as the feed solvent for the SMB system, but probably not forthe SMB eluent. Unlike the evaporators in the conventional processes,the evaporator in the present purification does not need to removeglycerol, only the lower boiling diols. This is because these lowerboiling diols tend to retain on the SMB chromatographic resin, elutingalong with the HTO, hence causing purity problems.

Isolation and purification of 1,2,5,6-hexanetetrol (HTO) by means of acombined process of evaporation and simulated-moving bed chromatography(SMBC) using an industrial grade resin has advantages over conventionalprocesses. In part, the present invention contributes to a refinement ofchromatographic separation techniques for difficult to purify organicspecies. These advantages include, for examples, cost savings andprocess efficiency associated with a continuous single-step separationmethod which more easily lends itself to high throughput automation, incontrast to the conventional need to employ multiple batch or semi-batchdistillations. Another advantage is the ability to collect HTO productat a greater yield and purity. The inventive approach compares favorablyto conventional approaches, in that it can be more efficient and costeffective than current processes.

According to a feature of the invention, we adapt liquid chromatography(LC) techniques to purify in a single operation a stream of 1,2,5,6-HTOfrom the large majority of other contaminants that are typically foundin a hydrogenolysis reaction mixture. LC typically utilizes differenttypes of stationary phases (i.e. sorbents) contained in columns, a pumpthat moves the mobile phase and sample components through the column,and a detector capable of providing characteristic retention times forthe sample components and area counts reflecting the amount of eachanalyte passing through the detector. Analyte retention time variesdepending on the strength of its interactions with the stationary phase,the composition and flow rate of mobile phase used, and on the columndimensions. Here, relatively large diameter columns and large particlesizes are employed to avoid pressure.

One may elute the chromatographic column with a variety of solvents,including for example, deionized (DI) water, methanol, butanol,isopropanol, simple C₁-C₄ aliphatic alcohols, or a mixture of these.Typically, the elution is with DI water alone. If a mixture of DI waterand alcohol is used, the water and alcohol may be present respectivelyin a ratio in a range from about 50:1 to 1:50 (e.g., 40:1, 35:1, 25:1,20:1, 12:1, 10:1, 5:1, or 1:30, 1:25, 1:20, 1:10, 1:8, etc.).

Lastly, one can perform another evaporation to remove excess water andeluent to collect the isolated 1,2,5,6-HTO as a solid if desired. Theparticular yields and purity of the separated 1,2,5,6-HTO can varydepending on the operational conditions. Nonetheless, according toembodiments of the present process, one can achieve about at least40-45% wt./wt. yield, and about 70-75% purity. Typically, the yield ismuch higher, such as reported in Table 4, below. In general, examples ofyield can range from about 50% or 55% wt./wt. to about 92% or 95%wt./wt., inclusive. More typically, the yield is in a range from about60% or 65% wt./wt. to about 88% or 92% wt./wt. (e.g., 63%, 68%, 70%,75%, 80%, 85%, 90% wt./wt.). Typically, the level of purity is about 80%or 85% to about 97% or 99.9%. More typically, the level of purity isabout 86% or 87% to about 96% or 98%.

B.—Resin Materials

As stated previously, a variety of methods have been explored for thepurification of 1,2,5,6-HTO including reactive extraction, distillation,and crystallization but each has met with problems. To overcome suchproblems, the present invention can employ either functionalized ornon-functionalized resins. In certain embodiments, thenon-functionalized resins appear to perform better. Non-functionalizedresins do not bind the different species by means of an ionic charge;rather, non-functionalized resins work by a balance of hydrophilic andhydrophobic affinities. In the embodiments described, the adsorbentresins are unmodified and considered to be hydrophobic resins. Thus,hydrophobic organic species can bind to them and be retained in aqueoussystems.

When a resin is not functionalized, the pH range of the input materialcan be in a range from about 0 to about 14. Typically, fornon-functionalized resins the pH is about 5 to about 8, and desirablyabout 6.5 to about 7.5. When the resin is acid functionalized, anadjustment of the pH of the input material may be necessary for thepolyol to have an affinity for the resin. Hence, the post-evaporativehydrogenolysis reaction mixture should be acidic, with a pH value ofless than 7. For acid functionalized resin, the reaction mixturetypically will have a pH of about 2.5 to about 5.8 or 6.5, moretypically about 5.5-6.0. Similarly, an adjustment of the pH of the inputmaterial may be needed for base functionalized resins. In suchsituations, the post-evaporative reaction mixture will have a pH in arange of about 7 to about 14. Typically, this pH range is about 7 toabout 9.5, and desirably about 7 to about 7.5.

In some embodiments, a type of resin employed in the separation of HTOcan be classified as adsorbent poly(styrene-divinyl benzene) (PS-DVB)resins. The polystyrene is crosslinked with divinyl benzene. PS-DVBresins are an attractive adsorbent for extraction and separation ofvarious types of compounds due to its stability over the pH range of1-14. PS-DVB resins are known to have hydrophobic surfaces that highlyretain non-polar compounds while poorly retaining polar compounds.

Hydrophobic-type PS-DVB resins are commercially available from a varietyof vendors (e.g., Dow Chemical Company, Rohm & Haas Co., MitsubishiChemical Corporation, Purolite Corporation, Lanxess Corporation, etc.).Depending on the manufacturer and the particular specifications of eachtype of resin, the resin can have a variety of different pore sizes andsurface areas, which can affect the physical and chemical nature of theresins, the quality of the separation and therefore the temperaturesrequired for the different protocols. One can use a resin that has asurface area in the range between about 120 m²/g or 150 m²/g up to about1100 m²/g or 1200 m²/g. Typically, the surface area of the resin is inbetween about 150 m²/g or 200 m²/g to about 800 m²/g or 1000 m²/g. Inparticularly adapted resins for certain organic solutions (e.g., cornsyrup, fruit juices, HFCS, polyphenols, or natural extracts), the resinhas a surface area of about 250 or 300 m²/g to about 600 or 750 m²/g.The average pore diameter can range between about 50 Å or 100 Å to about600 Å or 700 Å; typically between about 100 Å or 150 Å to about 450 Å or500 A. The mean diameter of the resin particles may range between about300 μm or 350 μm to about 750 μm or 800 μm; typically, between about 400μm or 500 μm to about 650 μm or 700 μm. The resins exhibit porosity inthe range of about 0.90 or 0.95 ml/g to about 1.40 or 1.52 ml/g;typically about 0.97 ml/g to about 1.18 or 1.25 ml/g.

As the adsorbent resins exhibit non-polar or hydrophobic tendencies,this means that they preferentially adsorb the more hydrophobic organiccompounds that are dissolved in water relative to polar compounds. Forinstance, a class of commercial ion-exchange resins from Rohm & Haas isAMBERLITE™ XAD™ polymeric adsorbents, which are very porous sphericalpolymers based on highly crosslinked, macroreticular polystyrenepolymers. Their high internal surface areas can adsorb and then desorb awide variety of different species depending on the environment in whichthey are used. For example, in polar solvents such as water, polymericadsorbents exhibit non-polar or hydrophobic behavior and can adsorborganic species that are sparingly soluble. This hydrophobicity is mostpronounced with the styrenic adsorbents. (In comparison non-polarsolvents, such as hydrocarbons, etc. most adsorbents exhibit slightlypolar or hydrophilic properties and so will adsorb species with somedegree of polarity. This polarity is most pronounced with the acrylicadsorbents and the phenolic adsorbents.)

In the examples and embodiments described herein, four commerciallyavailable, industrial grade resins, are chosen based on their divergentphysical characteristics, in order to screen adsorption properties forsorbitol and 1,2,5,6-HTO. Table 1, summarizes some of the physical andchemical attributes of the AMBERLITE™ brand, Optipore™ brand, and Dowex™brand resins. These four resins respectively are representative ofnon-functional, strong base/anion, and strong acid/cation resinsmaterials. Two non-functionalized resins, one mono-dispersed (XAD1600N)and one having Gaussian particle size distribution (V493) and twofunctionalized monodispersed resins, one strongly basic (1X8) and onestrongly acidic (Dowex 99/310) are selected. Three of the resins,XAD1600N, Dowex 99/310, and Dowex 1X8 were designated chromatographicgrade, the fourth (V493), was a highly cross-linked resin (temperaturefunctional −15° C.-25° C.) used for adsorption of low level volatilesfrom industrial vapor streams. (Hence, not a conventionalchromatographic resin material.) The mean diameter particle size of theresins can range from about 200 μm to about 850 μm. Typically, theparticles are in a range from about 250 μm to about 500 μm, anddesirably about 300 μm to about 450 μm.

TABLE 1 Characteristics of Resin Materials Moisture Particle CrosslinkExchange Retention Surface Particle Size Size Density Capacity CapacityArea Porosity Density Resin Functionality Distribution (μm) (%) (eq./L)(%) (m²/g) (cc/g) (lbs./cu.ft) Amberlite Non- Monodispersed 400 ≦10 n/a66-73 ≧800 ≧1.4 64 XAD1600N functionalized Dowex Type I strongMonodispersed 300 8 1.2 43-48 — — 44 1X8 base anion Optipore Non-Gaussian 300-850 ≧10 n/a 50-65 >1100 1.16 21 V493 functionalized DowexStrong Acid Monodispersed 310 5 >1.5 60-63 — — 51 Monosphere 99/310 *Allresins are polystyrene cross-linked with divinyl-benzene.

Other commercially available polystyrenic adsorbent resins, such asPuroSorb™ PAD adsorbents from Purolite, are made from clean monomers andhave high surface areas that are free from any contaminants such assalts, metals and other minerals, making them especially suitable forfood and pharmaceutical uses. However, such resins appear not to havebeen proposed or adapted for industrial separation of products fromsugar-alcohol hydrogenolysis, in particular for HTO.

C.—Continuous Separation—Simulated Moving Bed Chromatography

We envision that the present separation process can be readily adaptedfor use in simulated-moving bed chromatographic systems. An embodimentthat uses the present process makes feasible and commercially efficientthe separation of 1,2,5,6-HTO from other polyols on non-functionalizedresins using simulated-moving bed (SMB) chromatography. SMBchromatography utilizes a column bed containing the stationary phaseresin segmented into a plurality of column segments, which are moved ina countercurrent direction relative to the input flow of the movingphase sample and eluent. The segments of the column in the SMB apparatusare typically mounted on a carousel beneath input ports for sample andeluent and output ports for raffinate and product. Once properlyconfigured for a given separation, a SMB chromatographic separation canbe run continuously with a constant flow of feed being input into oneport, a constant flow eluent entering a second port, a constant flow ofraffinate being withdrawn from a third port, and a constant flow ofproduct being withdrawn from a fourth port. SMB chromatography can thusbe optimized to purify a stream of 1,2,5,6-HTO in a continuous fashion.Pulse tests discussed in the following section provide a basis toevaluate different conditions and resins for application in SMBchromatography.

FIG. 3 shows the results of a typical pulse test for the separation of1,2,5,6-HTO and sorbitol, and the relative effectiveness of the presentprocess to separate various different kinds of polyols or organicmaterials. For instance, the resolution for unreacted sorbitol,glycerol, erythitol, and threitol from 1,2,5,6 HTO in the hydrogenolysisreaction mixture can be achieved in a continuous chromatographic system.Persons of skill in the art understand that the separation performanceof other particular resins may be either better or worse than that whichis shown in the present illustrative results, and should be adjusted ineach individual case may dictate.

In FIG. 4, a pulse test result is divided into zones in order totranslate the pulse test separation to a continuous simulated moving bedsystem (SMB). Theoretical zone flow rates for adaptation to a SMBseparation method are determined from the pulse test, as detailed inTable 2. Table 3 shows the actual flow rates for zones adapted to a 12column, combined 500 cc, carousel-type, SMB chromatography system,loaded with a Gaussian non-functionalized resin (V493), configuredaccording to the diagram in FIG. 5. According to this embodiment, thesorbitol hydrogenolysis reaction mixture thin-film evaporative (TFE)distillate bottoms, processed according to the method detailed above,were diluted to approximately 30% wt. in deionized water and fed intothe SMB system depicted in FIG. 5, which was run continuously at roomtemperature (˜18-22° C.), with a fifteen minute step time, for 9.25hours, or three full rotations. The raffinate and extract werecollected, sampled and analyzed according to the method detailed above.The yield and purity of 1,2,5,6-HTO and sorbitol recovered according tothe present process were calculated and summarized in Table 6. The yieldof HTO and sorbitol achieved respectively is 88.0% and 99.6%. The purityof each compound respectively is 99.6% and 88.8%.

TABLE 2 Zone flows translated from pulse test results Zone Zone flows(mL/min) 1 7.00 2 2.50 3 3.25 4 1.00

TABLE 3 Pump flows for SMB translated from zone flows from pulse testPump pump flows (mL/min) pressure (psi) Configuration Eluent 6.00 9-11 2Enrich 2.50 13 3 Feed 0.75 11.00 5 Reload 1.00 8 2

TABLE 4 Yield and purity from the continuous SMB chromatographyexperiment 1,2,5,6-HTO Sorbitol (unreacted) Yield: 88.0% 99.6% Purity:99.6% 88.8%

Depending on the chemical and physical characteristics of the resinmaterials employed in the chromatographic separation, the resinmaterials may be subject to an operational temperature that ranges fromabout 10° C. or 15° C. to about 95° C. or 100° C., so long as themechanism of chromatography is not adversely interfered with to impedeflow. Typically, the temperature is at about ambient room temperature orin a range from about 18° C. or 20° C. to about 75° C. or 90° C. (e.g.,22° C., 27° C., 30° C., 35° C., 40° C., 45° C., 50° C., 55° C., 60° C.,65° C., 70° C., 78° C., 80° C., 85° C.). The temperature range can befrom about 15° C. or 20° C. to about 88° C. or 100° C. for thenon-functionalized resins. The temperature range can be from about 17°C. or 20° C. to about 50° C. or 60° C. for the functionalized resins.

Table 5 presents operational ranges flow rates as prescribed accordingto certain embodiments, but which may vary and can influence theoperational parameters of the SMB chromatography.

TABLE 5 Flow rate as written: Zone Flow rate ST Col. vol. BV (#)(mL/min.) (min.) (mL) (mL/mL) 1 6.88 15 43 2.40 Raff. 4.39 15 43 2 2.4915 43 0.87 3 3.24 15 43 1.13 Prod. 2.24 15 43 4 1.00 15 43 0.35

Expressed generally, Table 6 shows the flow rate for an amount ofmaterial that can be processed when constant bed volume (BV) and columnvolume is used, and step-time (ST) is variable. When the time intervalthat each column dwells between changing position in the SMBC changesfrom about 5 minutes to 15 minutes to 30 minutes, the flow rate for eachzone of the SMBC decreases proportionately for each step time.

TABLE 6 Flow Rate for each Zone of SMB (ST) Flow Zone (mL/Min.) 1 Raff.2 3 Prod. 4 ST  5 min. 20.6 13.2 7.5 9.7 6.7 3.0 (min.) 15 min. 6.9 4.42.5 3.2 2.2 1.0 30 min. 3.4 2.2 1.2 1.6 1.1 0.5

Alternatively, the flow can be expressed in terms of bed volumes (BV)for use in potential industrial scale operations. Table 7 shows theparameters for flow rate range when the step time (ST) and column volumeare constant and BV is variable—Low (0 to 3 BV), Medium (>3 to 8 BV),and High (>8 to ≧10 BV).

TABLE 7 Flow Rate for each Zone of SMB (BV) Zone Flow 1 Raff. 2 3 Prod.4 BV Low 4.6 2.4 2.2 2.6 2.0 0.6 Med. 6.9 4.4 2.5 3.2 2.2 1.0 High 8.65.7 2.9 3.7 2.0 1.7

As the data from FIGS. 3 and 4 suggest, successful separation of1,2,5,6-HTO from the other polyols and unreacted materials in thehydrogenolysis product feed tends to occur within a range of about 1 bedvolume to about 3 bed volumes. Nonetheless, this does not necessarilylimit the process as various factors, such as flow rate, feedconcentration or loading can affect the purity of the target compoundeluent.

In operation, certain selectivity capacity parameters should bemaintained. For instance in the pulse test targets, the peaks shouldoverlap significantly while maintaining good purities within theleading-edge and trailing edge regions. This facilitates maximumproductivity potential. For most economical SMB operation, it isdesirable that the target compound (all peaks) should elute within about1 to 3 BV. (See, Pynnonen, B., et al, Evaluate SMB Chromatography forYour Separation. Chemical Processing [Online] 2010

http://www.chemicalprocessing.com/articles/2010/079.html.) Selectivityshould be greater than (>) 2 for reasonable productivity. (See, Cox,Geoffrey B., Simulated Moving Bed Chromatography and Chiral Compounds,ISPE, Toronto, Sep. 29, 2005.)

Section III—Empirical

The present invention is further demonstrated by the following example.

A.—Feedstock Generation

Experiments with heterogeneous metal catalysts in continuous flow,trickle bed reactors, at the 30 cc and pilot scales, have shown efficacyfor the synthesis of 1,2,5,6-HTO from sorbitol. D-sorbitol 35% indeionized water with 0.5-1.0% wt sodium hydroxide co-catalyst was fedinto a 14 L trickle bed reactor. The reactor was packed with 14 L, 5% wtnickel 1% wt rhenium on carbon and used, along with flow rate, tocalculate liquid hourly space velocity (LHSV, hr⁻¹) of the feed.Sorbitol solution was fed into the 165° C.-200° C. reactor at 0.5-1.0hr⁻¹, under 1800 psi H₂ flowing at 20 SCFM. The reactor product wassampled and prepared by derivatizing with pyridine and acetic anhydrideat 70° C. and analyzed using a J&W DB-5 MS UI column (30m×0.25 mm×0.25um) on an Agilent 7890 equipped with an FID detector. Samples wereanalyzed for water using a Mettler Toledo volumetric Karl Fischerauto-titrator. Carboxylate analysis was performed with a Showdex SH-1011strong acid ion exchange analytical column (300×7.8mm) on an Agilent1260 HPLC equipped with a diode array detector at 210 nm.

According to an embodiment, the method of purifying 1,2,5,6 hexanetetrolfrom a reaction mixture containing HTO and other byproducts of ahydrogenation reaction of a sugar alcohol and/or a mono- ordi-dehydrative product of a sugar alcohol, involves:

-   -   a. contacting the reaction mixture with a strong acid ion        exchange resin to obtain a first eluent fraction depleted of        cationic species;    -   b. contacting the first eluent fraction with a strong basic ion        exchange resin to obtain a second eluent fraction depleted of        anionic species;    -   c. evaporating the second eluent fraction under vacuum and        retaining a first bottoms fraction depleted of water, volatile        alcohols and lower boiling diols;    -   d. subjecting the first bottoms fraction to a thin film        evaporation and retaining a second bottoms fraction depleted of        glycerol;    -   e. contacting the second bottoms fraction with a        non-functionalized chromatography resin, wherein the resin is        loaded into a simulated moving bed chromatography apparatus;    -   f. eluting the chromatography resin with deionized water; and    -   g. collecting a fraction enriched in HTO as compared to said        hydrogenation reaction mixture.

Derived from C₆ sugars, the sugar alcohol can be for example: sorbitol,mannitol, galactitol, fucitol, iditol, inositol, maltitol, and mixturesthereof.

In the present example, the hydrogenolysis product mixture was contactedwith an ion exchange (IX) resin before contacting the effluent with aresin material adapted for chromatography because the sorbitolhydrogenolysis reaction employed sodium hydroxide as a homogeneousco-catalyst along with the heterogeneous NiRe on carbon catalyst. The IXresin is used to purify the reaction mixture by removing ionic organicand inorganic species before the mixture is fed into the chromatographicseparation columns. In embodiments with other sorbitol hydrogenolysisreactions that do not use as a reagent or produce as a by-productsignificant ionic organic or inorganic species (e.g.: Raney copper, CuReon Zr, or Cu on carbon heterogeneous catalysts), the IX step prior tochromatographic separation would likely be unnecessary.

When an IX column is needed the ion exchange reaction can be either 1) asingle-step mixed-bed reaction, or 2) a two-step acid-first, base-secondreaction or the reverse base-first, acid-second reaction. The fractionof the ion exchange reactions can be concentrated by evaporation. Theevaporation method can be selected from the group consisting of vacuumevaporation, thin film evaporation (TFE), and a combination of bothvacuum and TFE. In certain embodiments, vacuum evaporation can beperformed at a temperature between about 110° C. to about 160° C., andunder a pressure in a range from about 100 Torr to about 10 Torr. TFEcan be performed at a temperature in a range from about 150° C. to about175° C. or 180° C., under a pressure from about 10 Torr to less than 1Torr (e.g., 0.1 Torr).

Table A summarizes the analyte distribution from the hydrogenolysisreaction. The reaction mixture was then passed over strong acid (Dowex88) and strong base (Dowex 22) ion exchange resins to remove sodium andcarboxylates respectively. The ion exchanged reaction mixture washeated, under vacuum, to remove water, volatile alcohols (methanol,ethanol, propanol) and finally propylene and ethylene glycols. Thebottoms from the evaporation, comprised primarily of sorbitol, glycerol,C₄/C₅-sugar alcohols, 1,2,5,6-HTO other triols and trace diols, was thenfed into a 2-inch Pope thin film evaporator (TFE) in the molecular still(internal condenser) configuration to remove glycerol. Thehydrogenolysis reaction mixture was preheated to 75° C. and fed at arate of 3.87 g/min, into the Pope still. The TFE skin temp was set at160° C., the bottoms temp was 95° C., the blade speed was 505 rpm, theinternal condenser was kept at 63° C., and the vacuum was held at 9.7Torr. The final distillate fractions were pooled and bottoms anddistillate analyzed. The bottoms fraction from the TFE, was used forresin experiments detailed below.

TABLE A Analyte Distribution of Streams from Sorbitol HydrogenolysisSeparation Hydrogenolysis PG Dist TFE Dist Analytes Reaction MixtureBottoms Bottoms Propylene glycol (%) 14.043 0.097 0.000 Ethylene glycol(%) 5.473 5.561 0.184 1,2,5,6-Hexanetetrol (%) 2.103 38.313 52.570Carboxylic Acids (%) 1.679 0.000 0.000 1,2-Butanediol (%) 1.629 0.0790.044 Sorbitol (%) 1.485 20.691 26.810 2,3-Butanediol (%) 1.236 0.0000.000 Glycerol (%) 0.783 14.370 9.410 Other Triols (%) 0.692 14.4868.617 Di-PG (%) 0.300 6.295 0.000 C-4 Sugar Alcohols (%) 0.070 2.3125.257 Other Diols (%) 0.060 0.563 0.000 C-5 Sugar Alcohols (%) 0.0280.525 0.546 Na (ppm) 6140 0.000 0.000 Water (%) 67.21 0.000 0.000Carboxylic Acids include: Glyceric, Glycolic, Lactic, Formic, Acetic,Levulinic, Propionic; C4-Sugar Alcohols include: Erythritol, Threitol;C5-Sugar Alcohols include: Xylitol, Arabitol; Other Diols Iiclude:1,2-Pentatediol, 2,3-Pentanediol, 1,2-Hexanediol; Other Triols include:1,2,3-Butanetriol, 1,2,4-Butanetriol, 1,2,5-Pentanetriol,1,2,6-Hexanetriol, 1,4,5-Hexanetriol, 1,2,5-Hexanetriol.

B.—Resin Screening—Beaker Tests

Four commercially available resins are used. They were filtered fromtheir bulk water using a Buchner funnel, dried under vacuum at roomtemperature in a Rotovap and weighed into beakers using an analyticalbalance. The thin-film evaporative (TFE) bottoms stream from Table A wasdiluted with deionized water and weighed into the beakers containing theresins using an analytical balance. Each of the four resins, was testedat increasing concentrations, to gauge adsorptive capacity. The beakerscontaining resin and hydrogenolysis TFE distillate bottoms were placedon a shaker, at room temperature and mixed overnight. The supernatantwas measured according to the methods described above.

According to an embodiment of the present invention, FIGS. 6 and 7 showthe percent (%) adsorption for each of the four resins described in theforegoing, at increasing loading, for sorbitol and 1,2,5,6-HTOrespectively. The figures contrast adsorbency and capacity of theresins.

In FIG. 6, the Type I strong base anion resin (Dowex 1X8) demonstratedthe best performance of the four kinds of sample resin materials foradsorbing sorbitol at about 32-78% per resin/sorbitol (g/g). This amountof sorbitol adsorbed is about 10% to about 20-28% greater than the nextbest performing resin material (AMBERLITE™ XAD1600N), which is anon-functionalized resin and it adsorbed about at about 17%-50%. The twoother remaining resins—non-functionalized (Optipore V493) and strongacid-functionalized (Dowex Monosphere 99/310)—performed comparable tothe XAD1600N material.

In FIG. 7, of the four resin materials tested, the material thatperformed the best for adsorbing 1,2,5,6-HTO appears to be a Gaussiannon-functionalized resin (Optipore V493), which adsorbed about 20% toabout 65% of the HTO per amount resin/HTO (g/g). This non-functionalizedresin adsorbed about 5-7% more than the next best performing materialwhich is a mono-dispersed non-functionalized resin material (AMBERLITEXAD1600N). The performance of the two remaining acid and basefunctionalized resins were comparable but at a little less (e.g.,difference of ˜5-10%) absorbency than that of the non-functionalizedresins.

Table B summarizes the data for each of the beaker tests. The results ofthese beaker tests suggested, surprisingly, that the Gaussiannon-functionalized resin (V493) had the best selectivity for 1,2,5,6-HTOand was selected for use in subsequent pulse tests.

TABLE B Data from Beaker Tests 1,2,5,6- Sor- Resin/ HTO bitol 1,2,5,6-Adsorp- Resin/ Adsorp- Resin* HTO tion Sorbitol tion Resin Type (g)(g/g) (%) (g/g) (%) XAD1600N Adsorb 25.44 65.95 57% 159.52 49% Mono-10.01 25.96 33% 62.79 27% dispersed 5.13 13.29 19% 32.15 15% 1X8 Strong25.50 66.11 46% 159.91 75% Base 11.35 29.44 39% 71.20 63% 5.24 13.59 16%32.87 35% V493 Adsorb 25.55 66.24 65% 160.21 43% Gaussian 10.28 26.6541% 64.47 26% 5.08 13.16 21% 31.83 13% 99/310 Strong 25.12 65.13 44%157.54 38% Acid 10.37 26.88 24% 65.02 19% 5.08 13.17 14% 31.86 11%

C.—Resin Screening—Pulse Tests

A slurry of non-functionalized adsorptive resin (V493), in deionizedwater was added to a #11 Ace Glass jacketed chromatography column (1.10cm ID×45 cm L) to the 43 cc mark. A solution of sorbitol hydrogenolysisreaction mixture thin-film evaporative (TFE) distillate bottoms,processed as described above, was weighed, using an analytical balanceand added onto the top of the resin using a polyethylene pipette. Thecolumn was capped with Teflon adapters and connected using 0.0625″Teflon tubing and Swagelok fittings to a peristaltic pump at theinfluent and an automatic fraction collector at the effluent. Deionizedwater was pumped through the column at room temperature using aperistaltic pump set to a flow rate of 1.45 mL/min. The effluent fromthe column was collected using an automatic fraction collector set tocollect a fraction every 60 seconds. A total of 120 fractions werecollected and every fifth fraction, starting at fraction one, wasanalyzed according to the procedure detailed above.

FIGS. 8 and 9 respectively present the results in selectivity andcapacity, relative to column loading for the separation of 1,2,5,6-HTOfrom sorbitol using a Gaussian particle distribution, non-functionalizedresin material (V493). The equation for concentration is: mg analyte/mLResin =Wt% Analyte*g Mixture/mL Resin (in column) At four differentconcentrations (5, 10, 20, and 40 mg/mL resin) the selectivity of theresin appears to be about 3.2, 2.8, 2.3, and 1.7 sorbitol/HTO,respectively. At the same concentrations, the resin capacity for HTOappears to be about 4.6, 4.0, 3.2, and 2.5, respectively. The data inFIGS. 8 and 9, suggests that as the loading of the feed ofhydrogenolysis product mixture increases the selectivity of the resinbetween sorbitol and HTO and the resin capacity for HTO decreasesrespectively. Hence, one should balance the volume or concentration ofthe feed loading and the selectivity of the separation as represented inthe pulse test of FIGS. 3 and 4, which shows the results of a typicalpulse test for the separation of 1,2,5,6-HTO and sorbitol, and indicatesthe relative efficacy of the separation of HTO from other polyols andunreacted sorbitol.

The calculations of capacity and selectivity can be expressedrespectively according to the following equations:

-   -   Capacity Factor—k    -   (also known as Retention Factor and Relative Retention)        k=(tR−tO)/tO    -   wherein,    -   tR=Retention Time of Peak,    -   tO=Retention Time of the Unretained Peak    -   Selectivity—a    -   Separation Factor (Using Capacity Factor)

a=k2/k1

-   -   wherein,    -   k1=Capacity Factor of Late Eluting Peak    -   k2=Capacity Factor of Early Eluting Peak

The present invention has been described in general and in detail by wayof examples. Persons of skill in the art understand that the inventionis not limited necessarily to the embodiments specifically disclosed,but that modifications and variations may be made without departing fromthe scope of the invention as defined by the following claims or theirequivalents, including other equivalent components presently known, orto be developed, which may be used within the scope of the presentinvention. Therefore, unless changes otherwise depart from the scope ofthe invention, the changes should be construed as being included herein.

We claim:
 1. A method of purifying 1,2,5,6-hexanetetrol (HTO)comprising: contacting a mixture comprising HTO and other C₁-C₆ alcoholsand polyols with a resin material adapted for chromatography, underconditions where HTO preferentially associates with the resin relativeto other components in the mixture; and eluting HTO from said resin witha solvent.
 2. The method according to claim 1, wherein said mixture is aproduct of a sugar alcohol hydrogenation.
 3. The method according toclaim 2, wherein said sugar alcohol is selected from the groupconsisting of: sorbitol, mannitol, galactitol, fucitol, iditol,inositol, maltitol, and mixtures thereof.
 4. The method according toclaim 2, wherein said sugar alcohol is sorbitol.
 5. The method accordingto claim 1, wherein said mixture is a product of a hydrogenation of monoor di-dehydration products of C₆ sugars, selected from the groupconsisting of isosorbide, isoidide, isomannide, 1,4-sorbitan,3,6-sorbitan, 2,5-sorbitan, 1,5-sorbitan, 2,6-sorbitan, and mixturesthereof.
 6. The method according to claim 1, wherein said mixturecomprises HTO, glycerol, volatile alcohols, sorbitol, water, and ionicspecies.
 7. The method according to claim 1, wherein said resin materialis a non-functionalized resin material
 8. The method according to claim1, wherein said resin material is either an acidic or basicfunctionalized resin in neutral form.
 9. The method according to claim1, wherein said resin material adapted for chromatography has a matrixcomposed of a polystyrene divinyl-benzene material.
 10. The methodaccording to claim 7, wherein said resin material has a Gaussianparticle size distribution.
 11. The method according to either claim 7or 8, wherein said resin material has a mono-dispersed particle size.12. The method according to claim 1, wherein said resin material has aparticle size in a range from about 200 μm to about 850 μm.
 13. Themethod according to claim 12, wherein said resin material has a particlesize in a range from about 250 μm to about 500 μm.
 14. The methodaccording to claim 1, wherein said resin material has an operationaltemperature in a range of about 15° C. to about 100° C.
 15. The methodaccording to claim 1, wherein an elution solvent is selected from thegroup consisting of deionized water, methanol, butanol, isopropanol,simple aliphatic alcohols, or a mixture thereof.
 16. The methodaccording to claim 1, wherein said method of purifying results in ayield of HTO of at least 60% wt./wt. at a purity level of at least 80%.17. The method according to claim 16, wherein said yield is at least 75%wt./wt. at a purity level of at least 85%.
 18. The method according toclaim 1, wherein said mixture contacts an ion exchange resin beforecontacting said resin material adapted for chromatography.
 19. Themethod according to claim 18, wherein said contacting with said ionexchange resin is performed either in a single step by contacting amixed-bed acid/base resin, or in two steps by contacting an acid resinfirst, then base resin second or the reverse with base resin first andthen acid resin second.
 20. The method according to claim 18, wherein afraction depleted of ions and containing HTO is obtained aftercontacting with the ion exchange resin and said fraction is concentratedby evaporation.
 21. The method according to claim 20, wherein saidevaporation method is selected from the group consisting of vacuumevaporation, thin film evaporation (TFE) and a combination of bothvacuum and TFE.
 22. The method according to claim 1, wherein resinmaterial adapted for chromatography is loaded onto a simulated-movingbed (SMB) apparatus.
 23. The method according to claim 22, wherein saidSMB apparatus is operated to perform continuous chromatographicseparation of HTO.
 24. A method of purifying 1,2,5,6 hexanetetrol (HTO)from a reaction mixture comprised of HTO and other byproducts of ahydrogenation reaction of a sugar alcohol comprising: a) contacting saidreaction mixture with a strong acid ion exchange resin to obtain a firsteluent fraction depleted of cationic species; b) contacting said firsteluent fraction with a strong basic ion exchange resin to obtain asecond eluent fraction depleted of anionic species; c) evaporating saidsecond eluent fraction under vacuum and retaining a first bottomsfraction depleted of water, volatile alcohols and lower boiling diol; d)subjecting said first bottoms fraction to a thin film evaporation andretaining a second bottoms fraction depleted of glycerol; e) contactingsaid second bottoms fraction with a non-functionalized chromatographyresin, wherein the resin is loaded into a simulated moving bedchromatography apparatus; f) eluting said chromatography resin withdeionized water; and g) collecting a fraction enriched in HTO ascompared to said hydrogenation reaction mixture.